Spectrally beam combined (SBC) fiber laser technology is established as the preferred solution for directed-energy laser weapon systems because it has demonstrated high E-O efficiency, improved SWaP (Space, Weight, and Power), and system robustness. An SBC high-power laser is composed of several fiber-laser modules (FLMs) whose beams are then combined into a single output beam. Each fiber-laser module contains a stack of pump-laser diodes that convert electric power to optical output. To maintain good system performance and efficiency, these pump-laser diodes need to be maintained at a precise temperature across all stacks. To meet SWaP requirements, it is preferable to design cooling plates with minimum pressure and flow requirements, while still maintaining tight temperature gradients for optimal pump-laser diode performance.
Some conventional temperature-control systems increase the flow rate by at least two times (i.e., 2× flow), and this additional flow rate increases system size and weight, which are key design discriminators at the system level. In high-power laser applications on platforms such as aircraft, for example, low coolant flow is desired in order to reduce overall weight and compact design. In fact, lower volumetric flow of coolant is preferred for some embodiments of many high-power laser systems.
U.S. Pat. No. 5,105,429 titled “MODULAR PACKAGE FOR COOLING A LASER DIODE ARRAY” by David C. Mundinger et al. (hereinafter, Mundinger et al.) issued Apr. 14, 1992, and is incorporated herein by reference. Mundinger et al. describe a laser diode array that includes a plurality of planar packages and active cooling. The laser diode array may be operated in a long duty cycle, or in continuous operation. A laser diode bar and a microchannel heat sink are thermally coupled in a compact, thin planar package having the laser diode bar located proximate to one edge. In an array, a number of such thin planar packages are secured together in a stacked configuration, in close proximity so that the laser diodes are spaced closely. The cooling means includes a microchannel heat sink that is attached proximate to the laser bar so that it absorbs heat generated by laser operation. To provide the coolant to the microchannels, each thin planar package comprises a thin inlet manifold and a thin outlet manifold connected to an inlet corridor and an outlet corridor. The inlet corridor comprises a hole extending through each of the packages in the array, and the outlet corridor comprises a hole extending through each of the packages in the array. The inlet and outlet corridors are connected to a conventional coolant circulation system. The laser diode array with active cooling has application as an optical pump for high power solid state lasers. Further, it can be incorporated in equipment such as communications devices and active sensors, and in military and space applications, and it can be useful in applications having space constraints and energy limitations.
U.S. Patent Application Publication 2002/0110165 titled “METHOD AND SYSTEM FOR COOLING AT LEAST ONE LASER DIODE WITH A COOLING FLUID” by David M. Filgas (hereinafter, Filgas) published Aug. 15, 2002, and is incorporated herein by reference. Filgas describes a method and system for cooling at least one laser diode with a cooling fluid which does not come into direct contact with the at least one laser diode. Liquid cooled heat sinks are provided on opposing sides of each laser diode. Individual modules are held together by a single holding mechanism allowing individual modules to be removed from the array for easy testing or replacement.
U.S. Patent Application Publication 2009/0185592 titled “LASER DIODE SYSTEM WITH REDUCED COOLANT CONSUMPTION” by Jan Vetrovec (hereinafter, Vetrovec) published Jul. 23, 2009, and is incorporated herein by reference. Vetrovec describes a high-power laser diode system offering reduced consumption and inventory of coolant. The invention provides coolant at a very high flow rate to a heat exchanger. A portion of the coolant flow downstream of the heat exchanger is separated and pumped by a fluid-dynamic pump back into the heat exchanger. The fluid dynamic pump is operated by a fresh coolant supplied at high-pressure. Because a substantial portion of the flow leaving the heat exchanger is recirculated back to the inlet, the amount of fresh coolant consumed is substantially reduced compared to a traditional laser diode system. This enables reduced size of coolant lines and results in a more compact and lightweight system. Other uses of the invention include cooling of devices requiring heat rejection at very high heat flux including photovoltaic cells, solar panels, semiconductor laser diodes, semiconductor electronics, and laser gain medium.
There is a need for improved temperature-control methods and apparatus for high-power laser systems.